They all did. They were working under duress when the Nazis came to power. Nearly every German was compelled to join the Party in order to have permission to work, and every occupation was regulated. Unions were Party apparatus. This had nothing to do with whether people espoused Nazism (many out of the general population did, of course) and the standbacks simply kept their silence (this was not a subject for the Peenemunde team). Von Braun at one point was arrested by the SS because they viewed his private studies on space flight to be a treasonous diversion of his assignment at Peenemunde. General Dornberger had to talk them out of it because von Braun was indispensable to the A-4 project, being the engineering team leader. In terms of national effort, military priority, and concentration of scientific expertise, the German rocket program was comparable to the U.S. Manhattan Project.

There wasn't any question of the U.S. "offering him a job." He advocated pre-emptive surrender to the Americans instead of to the Russians, so the assembled exodus was quite impressive. It was a windfall for Allied forces, the U.S. in particular. There was no question the U.S. would hang onto the Germans. Their goodwill was demonstrated by the fact that they did not put the Germans in prison for their accommodation. The Russians were a bit more austere in their treatment of the Germans they captured. That was the end of ballistic missile rocketry in Germany for all time. The U.S. was the only show in town for them and they were glad to leave the Nazi regime behind. They were all eventually sent to Huntsville, Alabama to work for the U.S. Army at Redstone Arsenal and learned to speak southern English with a German accent. Some others were sent off to U.S. aerospace manufacturers to spread the wealth around (e.g., Dornberger went to Bell Aircraft for ballistic rocket bomber studies and Krafft Ehricke went to Convair to champion the Centaur upper stage). They all became naturalized citizens (with maybe one exception, who was a closet Nazi and was later deported).